Light-based treatment of tissue is used for a variety of applications, such as hair removal, skin rejuvenation, wrinkle treatment, acne treatment, treatment of vascular lesions (e.g., spider veins, diffuse redness, etc.), treatment of cellulite, treatment of pigmented legions (e.g., age spots, sun spots, moles, etc.), tattoo removal, and various other treatments. Such treatments generally include delivering light or laser radiation to an area of tissue on a person's body, e.g., the skin or internal tissue, to treat the tissue in a photochemical, photobiological, thermal, or other manner, which can be ablative or non-ablative, among other properties, depending on the particular application.
Light-based treatment devices include various types of light sources, such as lasers, LEDs, flashlamps, etc. For example, diode lasers are particularly suitable for certain light-based treatments and devices for providing such treatments. Diode lasers are compact, as they are typically built on one chip that contains the major necessary components for light generation other than a power source. Further, diode lasers typically provide an efficiency of up to 50% or higher, which enables them to be driven by low electrical power compared to certain other lasers. Diode lasers allow direct excitation with small electric currents, such that conventional transistor based circuits can be used to power the laser.
Other characteristics typical of diode lasers include high temperature sensitivity/tunability, and a highly divergent beam compared to certain other lasers. Diode lasers typically emit a beam having an axis-asymmetric profile in a plane transverse to the optical axis of the laser. In particular, the emitted beam diverges significantly faster in a first axis (referred to as the “fast axis”) than in an orthogonal second axis (referred to as the “slow axis”). In contrast, other types of lasers, e.g., fiber lasers, typically emit a beam having an axis-symmetric profile in the transverse plane.
Laser-based treatment devices typically include optics downstream of the laser source to scan, shape, condition, direct, and/or otherwise influence the laser radiation to the target tissue as desired. Such optics may include lenses, mirrors, and other reflective and/or transmissive elements, for controlling optical parameters of the beam, such as the direction, propagation properties or shape (e.g., convergent, divergent, collimated), spot size, angular distribution, temporal and spatial coherence, and/or intensity profile of the beam, for example. Some devices include systems for scanning a laser beam in order to create a pattern of radiated areas (e.g., spots, lines, or other shapes) in the tissue. For some applications, the scanned pattern of radiated areas overlap each other, or substantially abut each other, or are continuous, in order to provide complete coverage of a target area of tissue. For other applications, e.g., certain wrinkle treatments, vascular treatments, pigmentation treatments, anti-inflammatory treatments, and other skin rejuvenation treatments, the scanned radiated areas may be spaced apart from each other by non-irradiated areas such that only a fraction of the overall target area of the tissue is radiated during a treatment session. Thus, in such applications, there are generally regions of untreated tissue between regions of treated tissue. This type of treatment is known as “fractional” treatment (or more specifically, fractional photothermolysis in some cases) because only a fraction of the target area is irradiated during a treatment session.